We are studying the interaction of the pulmonary circulation and lymph drainage during lamb bypass with a non-occlusive pump and the spiral coil membrane lung. An awake sheep model of acute diffuse pulmonary vascular obstruction by 50 micron carbon microspheres has been developed. Right ventricular ejection fraction and end diastolic volume were measured by thermodilution techniques. Platelet destruction during bypass was evaluated during infusion of prostaglandin D2, a platelet activity inhibitor. Bypass will be performed after acute pulmonary vascular injury and effects on the pulmonary circulation measures. Pulmonary vascular observation by silicone polymer infusion and tissue clearing allows quantitation of vascular injury. BIBLIOGRAPHIC REFERENCES: Ketteringham, J.M., Zapol, W.M., Birkett, J.D., Nelson, L., Massucco, A., and Raith, C.: A high permeability, non-porous, blood compatible membrane for membrane lungs: in vivo and in vitro performance. Trans. Amer. Soc. for Artif. Int. Organs. 2l:224-232, 1975. Zapol, W.M., Schneider, R.C., Snider, M.T., and Rie, M.: Partial bypass with membrane lungs for acute respiratory failure (In) International Anesthesiology Clinics, Recent Advances in Respiratory Surgical Intensive Care 14:l, Little Brown & Co., Boston, 1976.